Electric discharge tube



W. DE GROOT ET AL April 25, 1933.

ELECTRIC DISCHARGE TUBE -Filed April 1, 1931' discharge tube Patented Apr. 25, 1933 ,UNITED STATES PATENT'OFFICE' WILLEM DE GROUT AND EN GBERT HARMEN BEERINK, OF EINDHOVEN, NETHERLANDS,

ASSIGNOBS, BY MESNE ASSIGNMENTS, TO GENERAL ELECTRIC COMPANY, A. COR- PORATION OF NEW YORK ELECTRIC DISCHARGE TUBE Application filed April 1, 1931, Serial 'No.'526,922, and in the Netherlands April 3, 1930.

Electric discharge tubes in which the discharge takes place in a vapour atmosphere are known already in various constructions. Generally known are at present, for example, the so-called mercury vapour tubes, i. 0. discharge tubes in which discharges can be produced in mercury vapour, owing to which ultraviolet rays are generated in thetubes which rays pass to the outside through the tube wall which consistsof quartz or similar material transparent to ultraviolet light, said rays being utilized for different purposes.

With the use of such discharge tubes it is a frequent objection that the vapour in which the discharge is roduced, attacks that portion of the wall 0% the tube, which is destined for the passage of the rays generated. Even if this Wall portion is not attacked by the vapour, one often encounters-more particularly when using the vapour of a not easily volatilizable substancethat this vapour condenses on' the said wall portion which is a serious drawback. Due to these two causes the transmission of the rays to be emitted throu h the wall portion in questionis considerab y reduced, owing to which the efficiency of the tube may considerably decrease.

The invention concerns an electric discharge tube in which the discharge takes place in an atmosphere containing a vapour, and it has for its obj ect to eliminate the said disadvantages. 1

In an electric discharge tube according to the invention a member acting as a chimney is arranged for this purpose above the path of discharge. During the operation of the the va or broughtinto the discharge pathis carried ofi by the member acting as a chimney, so that that portion of the wall of the discharge tube which surrounds the discharge path and throu h which the rays generated must pass to t e outside, is not exposed to the action of the vapour.

he said member may be given such dimensions that the vapour settles onthe wall of this member or combines therewith. It is also possible to lead the vapour with the aid of the member acting as a chimney to apart of the discharge tube Where the vapour may settle on a wall portion not destined for the passage of rays or may attack this portion. The discharge path may be located entirely outside the member acting as a chimney, however, it is preferable to provide the dischar e member.

A portion of the wall of the member acting as a chimney may conveniently be provided with apertures and be made, for example, of gauze. When the vapour flows throu h these apertures a large portion thereof Will be condensed.

If one wishes to produce the discharge in a vapour of a not easily volatilizable subpath, at least in part, within the said stance, it is advantageous to arrange this substance in the discharge path by providing. the tube with one or more anodes consisting of hollow bodies and having aperture cavities on the side facing the cathode. In the said hollow anodes may be provided the substance to be evaporated by the discharge established between the cathode and the hollow anodes.

The latter are conveniently arranged within the member acting as a chimney.

In order that the invention should be more clearly understood and more readily carried into effect it will be explained with reference no to the accompanying drawing which represents, by way of example, a discharge tube according to the invention.

Figure 1 represents a longitudinal section of the tube;

Figure 2 is a top view showing in detail the construction of an anode of the tube, and y Figure 3 is a side sectional view of the anode structure along the line 33 of Figure 2.

The discharge tube represented in Figure 1 serves for the generation of ultraviolet rays which can pass to the outside through the portion 1 of the wall of the tube, which portion consists of quartz or of another material transparent to ultraviolet rays. The wall portion 1 is sealed through the intermediary of some transition rings 2 to the wall portion 3 which consists of ordinary glass. The transition rings 2 are made in the known manner of different materials having mutually difierent coeficients of expansion.

The tube contains an incandescent cathode 4, for example a Wehnelt-cathode and two anodes 5 and 6 mounted on the pinch 8 by means of supporting wires 7 which, if necessary, are coated with an insulating substance. The two anodes consist of semi-cylindrical bodies. As shown in detail in Figures 2 and 3, theanode 6 consists of a hollow iron body which is open at its lower end. This hollow anode contains a magnesium rod 9 which evaporates under the influence of a discharge produced between the incandescent cathode 4 and the anode 6 so that the discharge takes place in magnesium vapour. It is evident that the anode 5 may also be constituted by a hollow body. With the tube shown in the drawing the anode 5 consists, however, of a solid iron body, so that when the discharge tube is operated'with a two-phase alternating current, the magnesium is direct 1y heated by the discharge only during half of each cycle. The anodes are surrounded by an insulating cap 10, for example of quartz, which extends past the lower ends of the anodes and which is provided with a partition separating the twoanodes.

In the discharge tube s arranged a cylindrical member 11 consistin for example, of ordinary glass. This cylin er, which is open at its lower end, is connected at itstop to a gauze-shaped ring 12 carried in its turn by a ridge 14 provided on the foot 13. The anodes 5 and 6 are located in the cylinder 11 the cathode 4 being arranged at the end 0 this cylinder.

In addition to magnesium vapour the discharge tube contains a gas preferably a rare gas such as argon, for example, at a pressure of 250 mms. During the operation of the tube the gas and vapour atmosphere heated by the arc discharge ascends through the cylinder 11 acting as a chimney. While ascending the vapour carried along comes into contact with the wall of the cylinder 11 owing to which a lar e portion of this vapour settles on this cylin er or combines with the material constituting the latter. After the tube has been operated for some time the wall of the cylinder 11 therefore becomes entirely blackened. Combining of the magnesium with the wall of the cylinder 11 is facilitated by the high temperature this wall assumes durin operation. The contact between the ascen ing current and the wall of the c linder 11 can be improved by arranging in t e axis of the cylinder one or more screens which extend as close as possible to the wall of the cylinder. Y p

The atmosphere charged with vapour subsequently emerges through the aperatures of the ring 12 from the cylinder 11, some of the vapour depositing on the member 12. The gas current subsequently attains the upper part of the discharge tube and returns through cylinder 11 and the wall of the discharge tube to the lower part of this tube. It is also possible that in the upper part of the dis charge tube some magnesium vapour is deposited. The portion 1 of the wall of the tube through which the ultraviolet rays generated by the magnesium vapour discharge must pass to the outside remains substantially free from deposited magnesium so that the transmission characteristics of this wall portion for the rays generated is not deleteriously affected. The discharge tube represented can be utilized until the supply of magnesium contained in the anode 6 has entirely been used up. This anode is given therefore such dimensions that the amount of magnesium is sufiicient for operating the tube for a considerable time. This supply is preferably so chosen as to be suflicient to operate the tube as long as is the length of life of the other components of the tube, for example of the incandescent cathode.

The member acting as a chimney does not need to have the shape of a cylinder. It is also possible, for example, to 've it a conical shape and sometimes it mayTie advisable to enlarge it at its lower end. In the discharge tube represented the discharge path is located within the cylinder 11 but it may also be located either entirely or partly outside this cylinder.

The discharge tube is suitable not only for obtaining a magnesium vapour discharge but it may also be utilized for producing a discharge i-in the vapour of another substance, more particularly of those substances which can not easily be volatilized and which would attack the wall of the discharge tube. If, for. example, the discharge is caused to take place in sodium vapour, it is possible to obtain a very strong source for the emission of visible light. What we claim is:

1. An electric discharge tube comprising at least two electrodes, a substance the vapour of which participates in the discharge, an open ended and solid wall member acting as a chimney for said vapour.

. 2. An electric discharge tube comprising at least two electrodes, a substance whose vapour participates in the discharge, an open ended and solid wall member acting as a chimney for said vapour, said member being so disposed in the discharge tube that the discharge path between said electrodes is adjacent to one end of said member.

3. An electric discharge tube comprising at least two electrodes, a substance whose vapourparticipates in the discharge and an open ended solid wall member acting as a chimney for said vapour, said member being so disposed in the discharge tube, that the the cylindrical space between the ing a multitude of discharge path between. said electrode is at least partly within said member.

4. An electric discharge tube comprising at least two electrodes, a substance whose vapour participates in the discharge. and a member acting as a chimney for said vapour, said member having a wall portion comprisapertures.

5. An electric discharge tube comprising at least two electrodes, a substance whose vapour-participates in the discharge and a member acting as a chimney for said vapour, said member comprising a wall portion of gauze.

6. An electric discharge tube comprising at least two electrodes, a substance whose vapour participates in the discharge and av acting as a chimney for.

cylindrical member said vapour the u per part of said member being provided with a multitude of apertures;

7. An electric discharge tube comprising a narrow lower portion and a wide upper portion, and containing at least two electrodes disposed in said lower portion, a substance whose vapour participates in the discharge and an open ended solid wall member acting as a chimney for said vapour, one part of said member being disposed in said lower portion, and another part in said upper portion.

8 An electric discharge tube comprising acyhndrical lower portion and a bulb-shaped upper portion, electrodes arranged in said cylindrical portion, a substance whose vapour participates in the'discharge and a member acting as a chimney for said vapour, said member being partly disposed within said cylindrical portion, the ast mentioned 9. An electric discharge tube comprising a cathode, and at least one anode consisting of a hollow. body, having a cavity on its side facing said cathode, a substance whose vapour participates in the discharge, and a member acting as a chimney for said vapour.

10. An electric discharge tube comprising at least two anodes and a cap of body containing substance adapted to vaporized, and a member acting as a chimney for the vapour of said su nce.

11. An electric discharge tube comprising a gas filling, an incandescent cathode and at least one anode, said anode consisting of a body provided with a cavity on its side facmg the cathode, said cavity containing a vaporizable substance, a member within the tube to act as a chimney for the vapour of said substance, said member comprising a vitreous cylindrical portion and a portion consisting of and containing at least two said cavity containing gauze, said anode being dishave signed our .tl-on and partly within said bulb-shaped porpart of saidmember belng provided with a plurality of apertures.

emission of ultraviolet rays, having an en,-

disposed within said member. 7 

